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. Author manuscript; available in PMC: 2013 Oct 26.
Published in final edited form as: Mol Cell. 2012 Sep 13;48(2):231–241. doi: 10.1016/j.molcel.2012.08.009

Figure 7. (p)ppGpp governs starvation-sensing negative feedback control of GTP levels via direct enzymatic inhibition, thus preventing death.

Figure 7

(p)ppGpp, produced from GTP(GDP) and ATP, directly inhibits the GTP biosynthesis enzymes HprT and Gmk to rapidly block de novo and salvage GTP biosynthesis. (p)ppGpp is induced (1) to low levels by increased GTP levels, to provide negative feedback control of GTP; and (2) to high levels by amino acid starvation, via activation of the main (p)ppGpp synthetase RelA, to decrease GTP levels. The regulation of GTP by (p)ppGpp is important for cell viability as high levels of GTP result in cell death.